§ 9.08 Out-of-Court Experiments

• Jurisdiction: United States

§ 9.08 Out-of-Court Experiments

Expert testimony is often based on out-of-court experiments.¹⁷⁹ Admissibility depends on whether the experiment was conducted under substantially similar circumstances as those involved in the case. Rule 403 governs the admissibility of out-of-court experiments: Is the probative value (which often depends on similarity) substantially outweighed by the danger of misleading the jury and the consumption of time. Note, however, that the "substantially similar standard is a flexible one which, even when construed strictly, does not require that all variables be controlled."¹⁸⁰

For example, the results of shotgun tests conducted to determine muzzle-to-target distance have been admitted in evidence.¹⁸¹ When a shot shell is fired, the pellets generally emerge from the muzzle grouped together and then disperse in an ever-increasing pattern as the distance from the muzzle increases. The closer the shotgun is to the target, the smaller the dispersion pattern. By firing a shotgun at different distances, the dispersion pattern for a particular distance may be ascertained and compared to the dispersion pattern present at the crime scene. The relevancy of these experiments depends on the extent to which the conditions existing at the crime scene can be replicated in the experiment. Because the dispersion pattern differs for different shotguns and different types of ammunition, the identical weapon and the same type of ammunition used in the crime typically are required. If the conditions are not substantially similar, the results are not admissible.¹⁸²

Courts often distinguish between experiments offered as a reconstruction of an event and those that merely illustrate general scientific principles: "[E]xperiments which purport to recreate an accident must be conducted under conditions similar to that accident, while experiments which demonstrate general principles used in forming an expert's opinion are not required to adhere strictly to the conditions of the accident."¹⁸³This distinction is sometimes difficult to draw:

[E]xperimental evidence falls on a spectrum and the foundational standard for its admissibility is determined by whether the evidence is closer to simulating the accident or to demonstrating abstract scientific principles. The closer the experiment gets to simulating the accident, the more similar the conditions of the experiment must be to the accident conditions.¹⁸⁴

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^[179] A lay witness may also be used to...